How do you use session variables in wordpress?

1. Add below code in function.php file

function register_my_session(){
    if( ! session_id() ) {
        session_start();
    }
}

add_action('init', 'register_my_session');

2. After that you can store value in session variable like

$_SESSION['something'] = $xyz

Replace:

global $wp_session;

With:

$wp_session = WP_Session::get_instance();

Make sure you add $wp_session = WP_Session::get_instance(); before you try to echo the variable on page 2.